The invention concerns a hydraulically-operable disk brake for bicycles or similar vehicles.
In the construction of automotive vehicles and motorcycles, hydraulically-operable disk brakes have been widely adopted. In bicycles, they are not as yet in use. A disk brake for bicycles in a mechanical design is known from DE 22 29 481 C3. In this case, the caliper is mounted on the frame in a manner capable of being shifted via two head screws that penetrate through appropriate holes in the frame, wherein rubber disks encircling the screws between the caliper and the frame ensure a pretensioning into an initial position. By means of an appropriate adjustment of the fastening screws, the position of the caliper with respect to the brake disk can be adjusted in a direction parallel to the axis in order to thereby equalize the distances between the brake linings and the brake disk. The operation is carried out mechanically via a rope and pulley arrangement which engages an operating lever. The operating lever is moved back into its initial position via a return spring. Such a mechanically operable disk brake requires high operating forces, in particular because of the high frictional resistances on the force path. Furthermore, there arise problems of adjustment because of the plurality of parts, which problems may be attributed to the aggregate manufacturing tolerances within the operating mechanism. The distance between brake disk and brake-lining part in the initial position must be preadjusted so as to be relatively large. Furthermore, there necessarily appear instances of tilting, since the shifting axis determined by the two fastening screws is distant from the braking axis defined by the two brake linings, and thus necessarily there appear tilting moments during braking.
A hydraulically-operable bicycle brake is known from DE 33 25 970 A1. Here, however, the brake linings do not act upon a brake disk but instead directly upon the wheel rim. Due to the large diameter of the rim, the forces that appear during braking are relatively small. The press-on forces of the brake linings are accordingly relatively small, and the tilting moments that must necessarily appear, due to the double-arm lever construction, are also not excessively large. However, rim brakes have systemic disadvantages, such as, for example, the problem-beset performance of the brake in case of moisture as well as the limited choice of materials for the rim. For instance, there hardly exists a rubber formulation which will provide a satisfactory braking action in connection with chromium-plated steel rims. This presents a significant problem in practice, as such rims are commonly used, particularly in the case of inexpensive bicycles.